Semiconductor integrated circuits (ICs), which are commonly referred to as chips, require a power supply to operate. For chips where high power efficiency is required a switch mode power supply is typically used as the power supply for the chip. Where high power efficiency is not required, a less costly linear power supply may be used. These power supplies are typically provided as a module on the chip, which receives an unregulated power supply from an external source such as a battery. The internal power supply module is powered from this external power supply, and in turn provides power to the rest of the chip.
A class of known power supply modules is able to operate in both switch mode and linear mode, with the operating mode being selectable according to the requirements of the chip in which the power supply module is used. Power supply modules of this type are used in many different chips, with each chip setting the operating mode of the power supply module. A difficulty arises with this approach, however, in that the chip must indicate to the power supply module which operating mode it must adopt before the core functional elements of the chip have been initialized (booted up). In practice this is often achieved by the use of a one-time programmable element in the chip, which is pre-set during production of the chip to hold a value indicative of the required operating mode of the power supply module. Thus, when the chip is powered up from an external power supply, the operating mode of the power supply module is determined by the value stored in the one time programmable element. This approach adds to the bill of materials cost of the chip, due to the additional cost of the one-time programmable element. The one-time programmable element also increases the physical size of the chip, whilst one or more pins on the chip must be reserved for programming the one-time programmable element during production. Additionally, the use of a one-time programmable element in this way adds an additional step (of programming the one-time programmable element) to the production process, and can lead to difficulties in post-production testing of the chip.